Neil Young -- Divorcing After 35 Years ... Split on Money, United About Son

Neil Young is bailing on his wife after over 35 years of marriage, but he's not turning his back on their son ... an adult with special needs.

The Rock and Roll Hall of Famer filed to divorce singer-songwriter Pegi Young, citing irreconcilable differences. They got hitched back in 1978, and separated this past April.

In his divorce docs, Young makes no mention of paying Pegi alimony ... but says they've agreed that both will continue to support their adult son, Ben, who has cerebral palsy. (Neil actually has two adult kids with CP ... the other is from a previous relationship.)